Duodenum Anatomy: Segments and Overview

Duodenum Overview

• The small intestine extends from the pylorus to the ileocecal junction.
• The duodenum is the first of three parts, followed by the jejunum and ileum.
• The duodenum is the shortest, widest, thickest-walled, and least movable part of the small intestines.
• It is a C-shaped tube approximately 25cm long.
• It is located in the epigastric and umbilical regions.
• It curves around the head of the pancreas and has openings for bile and pancreatic ducts.

Duodenum segments

• The duodenum is divided into 4 parts: superior, descending, horizontal, and ascending.
• The ampulla, specifically the first half of the superior part, is intraperitoneal.
• The remaining parts of the duodenum are retroperitoneal.

Superior (1st) Part

• It is 5cm long and begins at the pylorus, running upward and backward on the right side of the L1 vertebra.
• It contains the ampulla, also called the bulb which is the first half of this segment.
• it is located on the transpyloric plane.

1st segment, Superior (1st) Part relantions

• Anteriorly related to the liver and gallbladder.
• Posteriorly related to the lesser sac, gastroduodenal artery, bile duct, portal vein, and inferior vena cava.
• Superiorly related to the epiploic foramen.
• Inferiorly related to the head of the pancreas.

Descending (2nd) Part

• This part is 8 cm long and is located on the right side of the 2nd and 3rd lumbar vertebrae.
• The major duodenal papilla, located on the medial border, where the common bile duct and main pancreatic duct unite to form the hepatopancreatic ampulla and open to the papilla.
• The minor duodenal papilla, also on the medial border, is where the accessory pancreatic duct opens, if present.
• Anterior relations are the gallbladder, right lobe of the liver, transverse colon, and coils of the small intestine.
• Posterior relations are the right kidney and right ureter.
• Lateral relations are the ascending colon, right colic flexure, and right lobe of the liver.
• Medial relations are the head of the pancreas, bile duct, and main pancreatic duct.

Horizontal (3rd) Part

• The third segment is 8 cm long
• It courses horizontally to the left on the subcostal plane, at the lower margin of the pancreas.
• Anterior relations are the root of the mesentery (superior mesenteric vessels within it) and coils of jejunum.
• The posterior is closely related to the right ureter, right psoas major muscle, inferior vena cava, aorta, inferior mesenteric artery, and testicular (ovarian) artery.
• Superior relation is with the head of the pancreas.
• Inferior is closely related to the coils of jejunum.

Ascending (4th) Part

• This segment is 5cm long.
• This part courses upwards and is to the left to the duodenojejunal flexure.
• The duodenojejunal flexure is held in position by a peritoneal fold, the suspensory muscle of diaphragm (ligament of Treitz), attached to the right crus of the diaphragm.
• Anterior relations are the root of the mesentery and coils of jejunum.
• Posterior relations are to the aorta and left psoas major muscle.

Structure of Duodenum

• Mucosal folds are visible.
• Major and minor duodenal papilla are shown.
• The common bile duct and pancreatic duct form the hepatopancreatic ampulla, opening into the second part of the duodenum

Blood Supply

• Arterial supply from the superior pancreaticoduodenal artery, a branch of the gastroduodenal artery, and the inferior pancreaticoduodenal artery, a branch of the superior mesenteric artery.
• Venous drainage is through the superior pancreaticoduodenal vein, draining into the portal vein, and the inferior vein joining the superior mesenteric vein.

Lymph and Nerve Supply

• Lymph drainage occurs through celiac nodes and superior mesenteric nodes.
• Nerve supply is sympathetic and parasympathetic (vagus) via the celiac and superior mesenteric plexuses.

Peritoneal Relations

• Duodenal recesses include superior, inferior, paraduodenal, and retroduodenal recesses.